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Basic Helicopter Aerodynamics, 3rd Edition by Simon Newman, John M. Seddon

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Units

The metric system is taken as fundamental, this being the educational basis in the UK. Imperial units are still used extensively, however, particularly in the USA but also by industry and other organizations in the UK. For dimensional examples in the text and diagrams, therefore, those units are used which it is felt have stood the test of time and may well continue to do so. Often units in both systems are quoted; in other cases reference may need to be made to the conversion tables set out below. In either system, units other than the basic one are sometimes used, depending on the context; this is particularly so for velocity, where for example aircraft flight speed is more conveniently expressed in kilometres/hour or in knots than in metres/second or in feet/second. The varieties used in the book are included in the table.

Quantity Metric unit and symbol Imperial equivalent
Primary quantities:
Mass kilogram (kg) 0.0685 slug
Weight newton (N) 0.2248 pound (lb)
Length metre (m) 3.281 feet (ft)
Time second (s) 1.0 s (sec)
Temperature kelvin (K) Celsius (°C)
Temp(K) = temp (°C)+273.15
Derived quantities:
Weight (force) kilogram force
9.807 N (kg) 2.2046 lb
Density kg/m3 0.00194 slug/ft3
Pressure N/m2 0.0209 lb/ft2
0.1020 kg/m2
Velocity m/s 3.281 ft/sec
3.600 km/h 196.86 ft/min
1.941 knots
Acceleration m/s2 3.281 ft/sec2
Accel. of gravity 9.807 m/s2 (g) 32.2 ft/sec2
Power watt, N m/s (W) 0.7376 ft lb/sec
Metric horsepower ...

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